Mr Woo said yesterday he was followed by three trucks to a Shenzhen car park after he crossed the border. The truck and some documents were taken from him.

He rang the transport company to inform the owner and then left the site. Company owner Pik Yuet-lee rushed to the car park, in Shangshacun, but the attendants refused to allow her near the truck because they said the driver had left it in their care.

Ms Pik went to a local police station and two officers were sent to the car park to help her.

But the park workers threatened them and told them to leave. Police later found the car park belonged to the Shangsha Militia Group. Shangshacun is one of the most notorious red-light districts in Shenzhen and is widely known for gangster activities.

The police allegedly changed tack and accused Ms Pik of 'hiding essential information'. They said the case was a 'business dispute' and police should not be involved.

Representatives of the Hong Kong Drivers' Organisation yesterday visited Shenzhen and appealed to the local police, who said the car park workers had the right to hold the truck.

'The driver had told the car park workers to take good care of the truck before leaving. So it is the car park workers' responsibility to ensure no stranger can take the vehicle away,' a captain at Shatou police station said.

The captain then hinted that the militia group was 'very powerful' and said its members were better armed than the police.

'They have machine guns and canons ... They are even better armed than we are,' he told the Hong Kong representatives. Another policeman told the representatives that Shangshacun was 'special'.

Yiu Kwai, vice-chairman of the organisation, said he was shocked by the lawlessness of the city.

'It's clear that the police are afraid of the militia group,' Mr Yiu said.